A semantic feature is a notational method which can be used to express the existence or non-existence of semantic properties by using plus and minus signs.

Man is [+HUMAN], [+MALE], [+ADULT]
Woman is [+HUMAN], [-MALE], [+ADULT]
Boy is [+HUMAN], [+MALE], [-ADULT]
Girl is [+HUMAN], [-MALE], [-ADULT]

Intersecting semantic classes share the same features.

Some features need not be specifically mentioned as their presence or absence is obvious from another feature. This is a redundancy rule.